Fluid loss control or filtration control is an important property of drilling fluids. One type of fluid loss control additive used in water-based drilling fluids is water soluble polymers, particularly 2-acrylamide-2-methylpropanesulfonic acid (also known as TBAS) and/or N-vinyl pyrrolidone (NVP) comprising polymers that can be used for high pressure, high temperature applications. However, in drilling fluids with high salinity, i.e. the Cl− concentration is 150,000 mg/L to 180,000 mg/L, a single polymer does not provide good fluid loss control at high temperature (over 300° F.) and high pressure in high density (15 ppg or higher).
It would be advantageous to have high performance water-based drilling fluids with improved fluid loss or filtration control, particularly in drilling fluids for high temperature, high pressure, high salt concentration, and/or high density applications.